SYDNEY (Reuters) - Australia's unique duck-billed platypus
-- an egg-laying, furry animal with web feet that spends most
of its time underwater -- is in fact part bird, part reptile
and part mammal according to its gene map.

A team of international scientists released the platypus
genome on Thursday, saying its complex sequence would aid the
study of human evolution -- particularly the development of the
immune, nervous and reproductive systems.

"Its probably the most eagerly awaited genome since the
chimp genome because platypuses are so weird," said Jenny
Graves, head the Comparative Genomics Group at the Australian
National University.

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"Comparing us with the platypus means that we can say
something about our common ancestor, which was one of the
earliest mammals, so that means that we can ask questions about
what happened to make us mammals," said Graves, after a
briefing on the platypus genome, published in the journal
Nature.

The platypus represents the earliest offshoot of the
mammalian lineage, some 166 million years ago, from primitive
ancestors that had features of both mammals and reptiles.

When the platypus was first discovered, English scientists
regarded it to be an Australian joke, thinking someone had
stuck a duck's bill and feet onto an otter-like animal.

The platypus is classified as a mammal because it produces
milk, suckles its young and is covered in fur, but it also lays
eggs like a bird or reptile and males have poisonous spurs on
their hind legs like a reptile.

CLUES TO HUMAN EVOLUTION

The Nature paper analyzed the genome of a female platypus
named Glennie in Australia. Its genome contained roughly 18,500
genes, similar to other vertebrates.

The researchers found genes that support lactation, and egg
laying, and genes responsible for venom production, which
evolved from ancestral reptile genomes.

"You see genes that look reptile-like, genes that look
bird-like and genes that look mammal-like. Its a pretty amazing
picture," Rick Wilson, director of The Genome Center at
Washington University in St Louis, said in an interview. Wilson
directed the platypus genome report.

The platypus swims with its eyes, ears and nostrils closed,
relying on electrosensory receptors in its bill to detect faint
electric fields emitted by underwater prey.

The researchers found the platypus had genes that allowed
the platypus to detect odors underwater. Similar genes are
found in dogs and rodents that use smell to forage.

The scientists compared the platypus genome with human,
mouse, dog, opossum and chicken genomes and found that the
platypus shares 82 percent of its genes with these animals.

"It teaches us a lot about some of the biology that some of
our earliest common ancestors might have had, in terms of
immune systems and early nervous systems functions," said
Wilson.

"If you really want to understand why humans are or are not
resistant to particular types of infectious agents...you really
have to understand rudimentary systems like birds, reptiles and
monotremes like the platypus."

Scientists said platypus sex chromosomes may help study sex
determination in mammals and infertility in humans. It has 10
sex chromosomes, 5 male and 5 female. Humans only have one of
each.

Researchers at Stanford University's School of Medicine in
California said the genome of the platypus, which unlike other
mammals carries its testicles internally, allowed them to study
two genes that move testes into the scrotum in most mammals.

They said understanding this process may explain why testes
of about 30 percent of premature boys fail to descend properly.